Exemplary embodiments of the present invention relate to a semiconductor device, and more particularly, to a magneto-resistance element using a magneto-resistance change.
A dynamic random access memory (DRAM) is a representative memory device which has been widely used. A DRAM is advantageous in that it can operate at a high speed and can be highly integrated. However, a DRAM is a volatile memory which loses data when power is interrupted, and thus, requires a refresh operation to rewrite data upon its operation. Hence, a DRAM is disadvantageous in terms of power loss in comparison to non-volatile memory. Also, a flash memory with nonvolatility and high integration characteristics is disadvantageous in that its operating speed is low. In this regard, a magnetic random access memory (MRAM) which stores data using a magneto-resistance change is advantageous in that it has nonvolatility, can have high speed operation characteristics, and can be highly integrated.
More specifically, MRAM refers to a nonvolatile memory device which uses a magneto-resistance change according to a magnetization direction between ferromagnetic materials. Exemplary cell structures, which are widely adopted as an MRAM, include a giant magneto-resistance (GMR) element using a GMR effect, a magnetic tunnel junction (MTJ) element using a tunnel magneto-resistance (TMR) effect, a spin-valve element, and so on. To overcome the disadvantage of the GMR element, the spin-valve element reinforces a ferromagnetic layer with a permanent magnet and adopts a free layer as a soft magnetic layer. In particular, the MTJ element has high speed and low power characteristics. The MTJ element may be used as a substitute for a capacitor of a DRAM and is applicable in a low power device, a high speed graphic device, or a mobile device.
In general, a magneto-resistance element has a relatively small resistance when spin directions (magnetic momentum directions) of two magnetic layers are equal to each other, and has a relatively large resistance when spin directions (magnetic momentum directions) of two magnetic layers are opposite to each other. As such, bit data can be written to an MRAM by using the fact that the resistance of the cell changes depending on the magnetization state of the magnetic layers. An MRAM having an MTJ structure is exemplarily described below. In an MTJ memory cell, having a ferromagnetic layer—insulation layer—ferromagnetic layer stacked structure, when electrons tunneling through the first ferromagnetic layer pass through the insulation layer, used as a tunneling barrier, the tunneling probability changes depending on the magnetization direction of the second ferromagnetic layer. That is, the tunneling probability is highest when the magnetization directions of the two ferromagnetic layers are parallel to each other, and is lowest when the magnetization directions of the two ferromagnetic layers are anti-parallel to each other. For example, it can be considered that data ‘1’ (or ‘0’) is written when a resistance is relatively large, and data ‘0’ (or ‘1’) is written when a resistance is relatively small. One of the two ferromagnetic layers is referred to as a pinned magnetic layer, whose magnetization direction is pinned, and the other is referred to as a free magnetic layer, whose magnetization direction is reversed by an external magnetic field or electric current.
Meanwhile, in order to utilize magneto-resistance elements in practical applications, in particular, in order to apply magneto-resistance elements to memory devices, a difference in electrical conductivity must be great between a first case in which the electron spin direction of the pinned magnetic layer and the electron spin direction of the free magnetic layer are equal and a second case in which they are opposite to each other. Specifically, when electric current flows through a thin insulation layer between the pinned magnetic layer and the free magnetic layer, a magneto-resistance ratio between the first and second cases should be highly disproportional. In order to obtain a highly disproportional magneto-resistance ratio, a surface roughness of an interface between the pinned magnetic layer and the insulation layer and a surface roughness of an interface between the free magnetic layer and the insulation layer must be improved. In general, the surface roughness of these interfaces may be improved through a thermal treatment, but the magnetic layers may be demagnetized at high temperature.